High pressure cleaners - blowing hot and cold

28th of January 2015

When is a hot water high-pressure cleaning system required to remove dirt or soiling? And what types of applications can be tackled with cold water alone? Ann Laffeaty asks manufacturers of high-pressure cleaning systems about the pros and cons of cold versus hot.

Cold water delivered at high pressure is a highly efficient method of cleaning away a wide variety of substances from walls, floors and other surfaces. But certain types of soiling such as grease, oil and paint can be hard to remove using cold water alone which means an element of heat may need to be added. But hot water is more expensive to deliver and could potentially cause damage to surfaces.

So when would an operative choose hot water over cold? And what are the advantages and disadvantages of each type of system?

Cold water works well with specific types of dirt and soiling according to Andrew Caddick, Nilfisk-Advance’s senior group product manager for professional high pressure washers.“ Cold water can be used for removing the type of soil that contains no oil, grease or fats,” he said. “For example it will clean away substances such as animal waste, sand, mud, general dust and mineral dirt from surfaces. Customer groups such as agricultural workers, tradesmen and craftsmen plus people working in the building, construction and hospitality industries traditionally come up against situations where a cold water unit will be required.”

He says hot water pressure washers, on the other hand, are more effective at removing soiling with a grease, fat or oil content, even when used at similar pressures and flow levels. “Heavy industry and the automotive segment are traditionally more focused on hot water cleaners,” he said.

According to Caddick, cold water machines offer a number of advantages over hot water versions. “Hot water machines are usually heavier and less mobile, and the Initial purchase cost is higher,” he said. “Maintenance costs will also be higher due to the need to maintain a boiler instead of a simple motor-pump unit. And of course, heated water brings fuel costs.”

In some cases, he says, excessive heat can be counter-productive. “In the food industry where the waste to be removed will often contain proteins, for example, hot water increases the cleaning effect - but only up to temperatures of 56 degrees,” he said. “Above this temperature the cleaning efficiency decreases because the proteins will be ‘re-cooked’ and this causes them to stick to surfaces.”

Eventual pollution

He adds there are other circumstances in which hot water cleaners would not be appropriate. “A hot water machine that uses a diesel-fired boiler emits exhaust gases,” he said. “In certain segments such as hospitals and the food industry the use of such units is not authorised due to eventual pollution to the environment.”

Dibo managing director Pierre van den Borne agrees with Caddick that the lower costs of cold water machines is one of their chief advantages. “There is no need for any electricity or fuel to heat the water,” he said. “A hot water machine can also cause damage to a surface that is not heat-resistant. But professional cleaners will be sufficiently competent to correctly assess each job and prevent this.”

He says a number of factors will influence the choice of cold or hot water for high pressure cleaning. “We often see farmers clean their stables with cold water using a higher water throughput and less pressure so that they can rinse away the dirt,” he said.

“A typical use for hot water machines on the other hand is for the removal of oil or grease. And in fact most cleaners prefer working with hot water since it cleans more effectively at lower pressures. But it depends on the surface.”

Kärcher’s Linda Schrödter also cites lower procurement costs as one of the chief advantages of cold water machines. “They are also more compact and lightweight which makes them easier to handle,” said Schrödter. “And the fact that they are easier to transport means their place of use can be changed frequently.”

She says typical areas of use for cold water high pressure cleaners include the construction, automotive and farming industries. “But hot water cleaners are also suitable for use in these same sectors for specific tasks: for example, hot water will effectively remove greasy, oily or stubborn dirt in the automotive and construction industries while in agriculture it can be used to reduce the microbe count.”

According to Schrödter, disadvantages of cold water machines include a longer wait before cleaned areas are ready for further processing.“ Cleaning may also be less efficient when using cold water because congealed oils and grease do not emulsify as quickly,” she said. “In fact a cold water machine typically takes up to 35 per cent longer than a hot water machine to perform the same task because the dirt does not dissolve so readily, and this reduces economic efficiency.

“When using cold water, too, it is often necessary to add detergent in order to remove grease, oil, resins and proteins – and this adds to the cost and leads to environmental pollution. And unlike hot water, cold water does not reduce the microbe count.”

In fact she feels hot water is often the best choice on any surface that is resistant to heat – even on the delicate façades of older buildings. “The use of hot water can actually protect sensitive surfaces,” said Schrödter. “The same cleaning effect can be achieved with hot water as with cold, but at a lower working pressure. Heat energy is an important factor in the cleaning process since every 10°C increase in temperature doubles reaction speed.”

She says that when oil, grease or soot are dislodged by heat they become easier to remove, while the emulsification of oil and grease in water is accelerated using hot water. “Heated surfaces will also dry faster,” she said.

Even higher temperatures

According to Schrödter, water temperatures can be increased still further with no resulting damage to the surface provided higher temperatures are balanced against lower flow rates.“By reducing the water flow rate, cleaning can be carried out even at steam temperatures as high as 155°C,” she said. “With a combination of mineral-free steam and pressure, even the most stubborn dirt can be loosened and a high level of cleaning performance can be achieved without the use of chemical additives. The steam stage for example is perfect for removing bitumen coatings and other paint coatings as well as soot deposits, lichens and algae.”

Gentle cleaning

She says that higher temperatures are often a better option on delicate surfaces because heat allows them to be cleaned more gently. “It is important to ensure those parameters that affect the machine’s action are set correctly so as to avoid damage,” she adds.

According to Schrödter, factors to be taken into account when using a hot water pressure washer include the jet angle and nozzle type; the spraying distance; nozzle pressure; water flow rate and reaction time. And in any case, she adds, hot versus cold is not necessarily a black-and-white issue. “For the sake of energy efficiency, the water temperature on all our models can be varied on demand from between 20°C and 155°C as required,” she said. “Though in fact many types of soiling is easy to remove at around 60°C.”

Nilfisk-Advance’s Andrew Caddick agrees with Schrödter that cleaning efficiency is not simply a case of hot versus cold. “The end result will depend as well on the level of pressure and water flow and whether or not a detergent is used,” he said. “All these parameters can be combined to provide the optimal cleaning solution.”

And he adds high pressure cleaners delivering hot water can in some cases be the best and most cost-effective option. “For an application where greases, oils or fats need to be removed, tests have shown that a hot water unit can lead to a reduction in cleaning time of up to 50 per cent,” he said. “Using a machine with an equivalent water flow and motor size, this can significantly reduce the running costs even after taking into account fuel consumption.”

As an example he says that using pressures of 180 bar and cold water delivered at 1,100 litres per hour, an operative will be able to clean away oil and grease from a metal surface three times faster than if he or she were to use 720 litres of cold water per hour at the same pressure.

“However, they would be able to clean six or seven times faster still if they were to use 180 bar and 810 litres per hour heated to 60°C,” he said. “With this increased cleaning efficiency, total running costs will be significantly lower with a hot water cleaner than with a cold water unit. And this means that over the lifetime of a machine, the hot water unit would be the best choice economically.”

He adds that there are many applications where hot water does not significantly increase the efficiency of cleaning or where the effect of hot water can be offset by the use of cold water combined with a detergent.

“The goal is to reduce cleaning time for the user which will then reduce running costs,” said Caddick. “Our aim is to identify the best practice for each application.”

Dibo’s Pierre van den Borne agrees that cleaning can be speeded up using a hot-water unit. “However, higher temperatures have a negative influence on protein and synthetic material,” he said. “The surface needs to be both hot water- and pressure-resistant.” According to him cleaning with cold water tends to require the use of either higher pressures or chemicals. “Increasing the pressure saves time, but the pressure used should depend on the degree and the kind of pollution as well as the fragility of the surface that has to be cleaned,” he said.

And he adds that every cleaning job must be treated as an individual case. “The surface and the kind of pollution will ultimately have an influence on whether it should be cleaned with hot or with cold water,” he said. “There is no general rule that says cleaning has to be carried out one way or another.”